[tex]\it \ell = 30\%\ din\ L\ \Rightarrow \ell=\dfrac{\ \ 30^{(10}}{100}\cdot L\ \Rightarrow\ell =\dfrac{3L}{10}\ \ \ \ \ (1)\\ \\ \\ \mathcal{P}=2(L+\ell)=312\bigg|_{:2} \Rightarrow L+\ell=156 \Rightarrow\ L+\dfrac{3L}{10}=156 \bigg|_{\cdot10} \Rightarrow\\ \\ \\ \Rightarrow10L+3L=1560 \Rightarrow 13L=1560\bigg|_{:13} \Rightarrow L=120\ cm\ \ \ \ \ \ (2)\\ \\ \\ (1),\ (2) \Rightarrow \ell=\dfrac{3\cdot120}{10}=3\cdot12=36\ cm[/tex]
[tex]\it \mathcal{A}=L\cdot \ell=120\cdot36=4320\ cm^2[/tex]
[tex]\it R\breve aspunsul\ corect\ este\ \ a)\ \bf 4320\ cm^2[/tex]
